1. Technical Field
The present invention relates to the field of telecommunications trunk rerouting and, in particular, to the rerouting of intra-office digital signals, for example, for maintenance or circuit rearrangement purposes or in the event of an imminent or actual intra-office cable failure.
2. Description of the Relevant Art
It is known to reroute inter-office telecommunications trunks in the event of a failure or imminent failure or for maintenance purposes. For example, a restoration system known as FASTAR, which is described and claimed in U. S. Pat. No. 5,182,744, assigned to ATandT, is being utilized within the United States toll network to assist in the automatic rerouting of inter-office facilities. Inter-office telecommunications trunks connect central offices together via various means including satellite, microwave, wireless, coaxial cable, twisted pair cable and other means. Redundancy is often provided in inter-office trunking facilities that may be path diverse (for example, satellite, microwave, optical fiber, repeatered land line, submarine cable or other inter-office facility), equipment diverse or otherwise redundant.
Intra-office signal communication, that is, transport of a signal simply across a telephone central office, however, has developed over the years with a significantly less degree of equipment, facility or other redundancy. Inside a telephone central office, there exist frames of equipment that may be spread over multiple floors of a central office building with overhead cable racks in which intra-office cables have been lying for years. Satellite and microwave dishes which receive signals from all over the world may be mounted on top of the multi-story central office building. Cable vaults underneath the building provide access to land lines below ground level. Insulation can rot on and within cables layered in cable racks or run between building floors. Individual cable pairs of wires can short together, the copper wires break open, connectors can deteriorate or come loose and the like. Cables and cable connectors can succumb to aging, environmental changes, moisture and stress causing them to deteriorate. The placement of new cable layers upon layers of existing cable, bending cables around the central office and the weight of cables stressed due to floor-to-floor drops causes cable and cable connector deterioration over time. The failure of an intra-office trunk can mean not only the instantaneous disconnect of one or more calls but, with the loss of one intra-office transport means, the efficiency of the entire telecommunications network can become at risk. Intermittent problems due to the deterioration of a cable or cable connector can cause chronic problems for a customer""s service.
Referring to FIG. 1, a typical telecommunications network is shown and many terms such as intra-office, inter-office, subscriber line, central office (including local, tandem and toll offices) and the like will be defined. The North American numbering plan will be used by way of example and should not be deemed to be limiting on the scope of the present invention. Starting with a typical subscriber 101, subscriber 101 is connected to a local telephone central office by a subscriber loop or line 105. Line 105 may typically comprise a twisted wire cable pair (which may provide an asynchronous digital subscriber line connection). Line 105 may also comprise a wireless connection, for example, to a serving cellular service switch. In a cable telephony/television environment, line 105 may comprise a shared bandwidth portion of bandwidth provided via a hybrid fiber coaxial cable distribution system. Local central office 111 may be a wire center such as a #1 or #5 Electronic Switching System manufactured by Lucent Technologies serving several telephone exchanges.
Subscriber 101 may be in the 654 exchange of the 301 area code having the directory number 654-2321. Local central office 111 may be a wire center having several exchanges and will have intra-office trunks, for example, intra-office trunk 109 which can carry calls across the central office from one exchange to another exchange within the same central office to another subscriber, for example, subscriber 103 who may be in the 652 exchange of the 301 area code. Intra-office trunk 109 carries a signal across a central office in this example from one exchange to another. The interexchange, intra-office trunk is but one example of an intra-office trunk. Other examples will now be further described.
Subscriber 101 may wish to communicate with subscriber 153 in the 630 area code. As can be seen from FIG. 1, there are many alternative paths between local central office 111 serving subscriber 101 and local central office 149 serving subscriber 153 who is connected to office 149 by subscriber loop or line 151. Inter-office trunks are transport means for connecting central offices together. Examples of interoffice trunks include trunks 113, 115, 117, 123, 125, 133, 135, 137, 139, 141, 143 and 147. Subscriber 101 may be connected to subscriber 153, for example, via interoffice trunks 117 and 147. Another route might be via interoffice trunks 115, 143, 147. Another route might be via trunks 113, 123 and 141. Other routes are seen from the figure.
These alternative inter-office routes involve central offices that may not be within boundaries of a regional telephone operating company and, consequently, must involve an interexchange carrier (IXC) such as ATandT. The IXC operates and maintains tandem central offices and toll central offices one of whose functions is to provide switching or cross-connection between inter-office trunks. Tandem central office 127 connects toll offices 121 and 131 together or can connect a toll office to a tandem office, such as tandem office 145. The local exchange carrier (LEC) may also operate toll and tandem central offices, such as tandem office 145 that connects local central offices 119 and 149 together.
Telephone central offices have switching and cross-connect equipment. Many paths through an office are switched; many are not switched at all but merely cross-connected. An intra-office trunk within a toll or tandem office is defined as a telecommunications channel between two pieces of equipment within the same toll or tandem office that may or may not be switched. With reference to toll central office 121, for example, there may be an intra-office trunk or trunk group of channels that connect ports toward local central office 111 to ports toward tandem office 127. Looking at the combinations, there may be A-B, A-C, and A-D intra-office trunks, also, B-C, B-D and C-D intra-office trunks shown in FIG. 1 by dotted lines. In practice, some IXC toll offices may provide many more intra-office trunk groups than the six groups identified for toll office 121. These intra-office trunks may typically comprise pairs of wires carrying many digitally multiplexed channels. Wires go open, wires break and whole intra-office trunk groups of channels can fail when a single wire breaks or a connector fails. There is an opportunity to repair, replace or perform preventative maintenance on connectors and the like on a routine basis. Thus, there is a need in the art for a system and method for rerouting intra-office trunks. Moreover, with digital systems such as T1 digital carrier systems where a single pair of wires may represent 24 DSO channels or T3 systems where a single pair of wires may represent 28 T1 channels, the problem becomes more complicated as all 24 DS0 or 28 T1 channels must be rerouted together and simultaneously in order to minimize service disruption. Moreover, it would be desirable if rerouting is effectuated as rapidly as possible after a determination of a necessity to reroute is made. Finally, it would be desirable if a rerouting of signals occur through the central office via alternative paths upon the detection and reporting, for example, of the event of an imminent or actual cable wire or connector that has open or shorted.
The problems and related problems of the prior art are solved according to the principles of the present invention by providing a method of rerouting an intra-office digital signal through a telephone central office comprising the steps of storing identification data for ports of first and second digital access and cross-connect systems, the ports being connected by an intra-office digital trunk, storing identification data for an alternative path from said first digital access and cross-connect system to said second digital access and cross-connect system, correlating identification data for said alternative path to said identification data for said intra-office digital trunk, determining availability of and displaying alternative path data responsive to display of identification data for said intra-office digital trunk, and rerouting said intra-office digital signal via said alternative path. A known transport maintenance alarm and surveillance system (TMAS) for monitoring digital access and cross-connect frames, digital test maintenance frames and other intra-office trunk related equipment within a central office and having an associated digital test maintenance station (DTMS), for example, that may be a Sun SPARC work station, may maintain such identification data and, with modified digital element maintenance software (DEMS), correlate the data in memory as a database. When an imminent cable failure is detected, for example, via a monitored burst of errors or when maintenance is required, the operator of a work station may be advised via display of the port identity of the failing digital signal port or port undergoing maintenance and of the availability of an alternative path through the office so that, for example, twenty-four DS0, twenty-eight T1 or more digital intra-office channels can be immediately and simultaneously rerouted.
For example, in an Alcatel cross-connect system embodiment, the software package according to the present invention (accessed, for example, via DEMS) operates within the same cross-connect system utilizing available spare ports within that system. The principles of the present invention can be extended to any central office having intra-office digital trunks for which alternative paths through the office exist including local central offices, tandem central offices and toll central offices. Moreover, the principles of the present invention may be applied to circuit rearrangement, maintenance reroute or restoration of failed or impaired services among other purposes. Other features of the present invention will be understood with reference to the accompanying drawings and to the detailed description of the invention which follows.